The present invention relates to a hydraulic press in general and to a hydraulic press having a precision controlled movable platen reliably to maintain desired movement velocities, parallelism and forming pressures in particular.
Hydraulic presses having a two-stage sequence of operation are well known in the art as shown in U.S. Pat. Nos. 3,540,081; 3,587,135; 3,606,638; 3,505,708; 3,697,212; 3,716,323, and in a Cincinnati Milacron Brochure on Plastic Injection Molding Machines. As exemplified by such teachings, these two-stage presses may include a movable platen initially rapidly cycled from an open position to a substantially closed pre-form position under low pressure, and then cycled from the pre-form position to a closed forming position under higher pressure. These presses may include various clamping mechanisms selectively to connect the movable platen to a central drive shaft or pull down rods, and still other exemplary clamping mechanisms used in the press art are shown in U.S. Pat. Nos. 3,941,141; 3,050,943; 3,603,248; and 3,756,145. These two stage presses do not provide the control over the movable platen that is necessary to provide the parallelism, forming speeds and part reliability required in certain industries.
In this regard, the press forming of certain materials requires specialized and exacting operational parameters to be employed in producing parts to tight dimensional tolerances and strength levels. These requirements have heretofore been difficult to achieve in cost effective manufacturing procedures because of the practical limitations of the machinery in the operative context of the materials forming environment. For example, some plastic materials are rather frequently formed into parts having not only intricate surface contours but also uniform cross-sectional strength standards. The mold forms and molding parameters may be empirically determined, but the known presses have been unable to satisfy these empirical determinations with the reliability and operational speeds preferred. This is caused from the presence of one or more of the following limiting factors: slowness in molding; lack of precise control over the movable platen; lack of parallelism between the movable and fixed platens; and lack of adjustment mechanisms immediately to compensate for loading and/or operational problems.
The principal object of the present invention is to provide a press that can closely and reliably control forming velocities, pressures and parallelism in rapidly performed operational cycles.
A further object of the present invention is to provide a movable platen that may be quickly driven along four pull down power rods between an elevated open position and a lowered reference position in which the movable platen is exactly parallel to the lower platen. This movement between the upper and reference positions is accomplished by fast acting, relatively low pressure piston-cylinder assemblies extending between a fixed base and said movable platen.
Another object of the present invention is to provide a high pressure forming stroke for a dimensionally reinforced movable platen by clamping the movable platen to the four pull down power rods in the reference position and by then driving the four pull down power rods under high forming pressure to bring the movable platen into mating engagement with the fixed platen. The high forming pressure is achieved by short stroke piston-cylinder assemblies respectively positioned under and simultaneously driving each of the four pull down power rods to lower the same, with such arrangement reducing the press height required and improving forming stroke control.
Still another object of the present invention is to provide precise control over the movable platen during its short forming stroke reliably to meet the operational forming parameters required by the material and mold shape being processed. This precise control may be accomplished by the drive and mechanical guidance structure cooperating with a feedback system. This feedback system continuously monitors the conditions occurring during the forming stroke of the movable platen and comparing such conditions to the preselected desired conditions. If correction is required, the feedback system controls the main and auxiliary hydraulic oil supply lines independently to adjust the oil supply to the high pressure cylinder or cylinders requiring correction while the other high pressure cylinders are simultaneously being supplied in accordance with normal requirements.
Yet another object of the present invention is to provide readily accessible and fail safe clamping structure selectively to secure the movable platen to the pull down power rods. To this end, a wedge ring clamping assembly is mounted on the movable platen for each pull down rod, and each assembly includes a single annular wedge ring operative to cam a plurality of segments into locking engagement with their respective pull down rod. The wedge ring cam surface and segment cam follower surfaces are cooperatively inclined at a self locking angle to provide fail safe clamps.
Other objects and advantages of the present invention will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.